The specific aims of this project are to empirically examine the factors which may be responsible for the rapidly increasing prevalence of obesity in the United States. The available data show that the prevalence of obesity has increased from 24.4 percent in 1960-1962 to 34.8 percent in 1988-1994. Obesity and sedentary life styles increase the risk of many chronic health conditions. Estimates of the health care costs of obesity in 1990 exceed $45 billion a year with an additional $33 billion spent on weight reduction products. Although the increase in the prevalence of obesity has been substantial, the reasons for this increase remain unknown and speculative. The development of policies to reverse this trend requires an understanding of the underlying behavioral processes. A model that focuses on the increase in time spent in market work will be developed. This model distinguishes between endogenous and exogenous determinants of obesity and sedentary life style. Between 1970 and l990, a typical two earner family increased market work by 600 hours a year, with little or no increase in income for many families. The theory asserts that the decrease in available home time has increased the demand for inexpensive, convenience food and has led to an increase in consumption of high caloric density food such as fast food. Similarly, the theory asserts that the decrease in available home time has increased sedentary leisure. Other factors which may have increased the prevalence of obesity include the reduction in cigarette smoking, the increase in fast food availability, changes in the relative price of fast food, increases in fast food advertising, aging of the population, and habituation to high caloric density food. The empirical work outlined in this application will employ three data collections. These data collections are: 1) the First, Second and Third National Health and Nutrition and Examination Surveys; 2) the Behavioral Risk Factor Surveillance System, 1984-1997, at both the aggregated and individual level; and 3) the National Longitudinal Survey of Labor Market Experience of Youth (NLSY), 1979 baseline and panels through 1997, the NLS Child-Mother File, and the new NLSY 1997 sample of youths. These data sets will be augmented with grocery, fast food, and cigarette prices and with fast food availability and fast food advertising.